The arrangement of shut-off valve devices on the brake pipe of a freight car normally includes an angle cock at the end of the car to open or close brake pipe communication between adjacent cars, and a cut-out cock interposed in a branch pipe leading to a brake control valve on the car and connected by a tee to the brake pipe, and cut-out cock serving to either open or cut out communication between the brake pipe and the brake control valve. It would be desirable to provide a single valve unit capable of performing the combined functions of the angle cock and cut-out cock.
In considering a possible valve device for accomplishing the object above noted, the concept of a four-way valve would serve the purpose, but the question remains as to which type of valve device, for example, spool, diaphragm, poppet, or ball, would best serve the purpose.
The spool type four-way valve is found objectionable because of restricted air flow capacity due to angled flow paths. To obtain sufficient flow capacity, the size of the valve device would have to be quite large and, therefore, impractical. Since the O-rings would have to be proportionately large, they would be susceptible to being blown out or dislodged from their grooves.
A diaphragm type valve device would entail undue complexities including three separate diaphragm covers, and because of the porting arrangement, would also result in poor flow capacity. Again, the flow capacity requirements would necessitate use of large diaphragms and, therefore, result in a larger than practical device.
The poppet type valve device would also be complex, characterized by poor air flow and having the same disadvantages as the diaphragm type construction. In addition, this type is susceptible to having foreign objects becoming lodged between the poppet valve seal and seat to cause undesirable leakage.